At the heart of a computer is an assembly that is referred to as a magnetic disk drive. The magnetic disk drive includes a rotating magnetic disk, write and read heads that are suspended by a suspension arm adjacent to a surface of the rotating magnetic disk and an actuator that swings the suspension arm to place the read and write heads over selected circular tracks on the rotating disk. The read and write heads are directly located on a slider that has an air bearing surface (ABS). The suspension arm biases the slider into contact with the surface of the disk when the disk is not rotating, but when the disk rotates air is swirled by the rotating disk. When the slider rides on the air bearing, the write and read heads are employed for writing magnetic impressions to and reading magnetic impressions from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
The write head includes at least one coil, a write pole and one or more return poles. When current flows through the coil, a resulting magnetic field causes a magnetic flux to flow through the coil, which results in a magnetic write field emitting from the tip of the write pole. This magnetic field is sufficiently strong that it locally magnetizes a portion of the adjacent magnetic media, thereby recording a bit of data. The write field then, travels through a magnetically soft under-layer of the magnetic medium to return to the return pole of the write head.
A magnetoresistive sensor such as a Giant Magnetoresistive (GMR) sensor or a Tunnel Junction Magnetoresistive (TMR) sensor can be employed to read a magnetic signal from the magnetic media. The magnetoresistive sensor has an electrical resistance that changes in response to an external magnetic field. This change in electrical resistance can be detected by processing circuitry in order to read magnetic data from the magnetic media.
The ever present need for increased data density requires the reduction of various sensor dimensions which can present challenges to sensor design, performance and magnetization. One parameter that can be reduced to improve data density is the gap spacing of the magnetic sensor, as this correlates to magnetic bit length and magnetic bit spacing. Reduction of this gap length in a traditional giant magnetoresistive sensor or tunnel junction sensor is limited by the need for various magnetic layers necessary for the performance of such a sensor. For example, pinning of the pinned layer structure requires the use of a relatively thick layer of anti-ferromagnetic material (AFM layer) and also requires a complex pinning layer structure such as an AP coupled structure that includes first and second magnetic layers that are anti-parallel coupled across a non-magnetic anti-parallel coupling layer, with one of the magnetic layers being exchange coupled with the AFM layer. The presence of these necessary layers increases gap spacing and reduction of the thickness of these layers is problematic. The thickness of these layers can only reduced so much without affecting sensor performance, reliability and robustness.
One type of sensor that shows promise in reducing gap spacing is a scissor sensor design. Such a sensor includes two magnetic free layers that have magnetizations that are biased in directions that are orthogonal to one another. In such a sensor, a pinned layer structure is not necessary so the complex, thick pinning structure can be eliminated. However, such sensor present challenges with regard to design and sensor performance, such as biasing of the two magnetic free layers. Therefore, there remains a need for a scissor sensor design that can provide a sensor that is practical to manufacture, while providing superior magnetic performance and reliability.